Also, when I try to decrease the buffer size, I PT stops and I get the dreaded window that says "increase buffer size". I'm currently running 256 for mixing, but can't increase sample rate for recording without system freezing up and increasing buffer size greatly.

So my question is what buffer size can I expect to get away with, or do I have to look deeper into my system to solve this problem.

Also, are they any Windows tweaks out there to improve system performance.

On my HD/Native rig, I tracked full bands all day long at a 64 buffer, so maybe your PC needs some serious tweaking(mine was on either a custom-built 6-core or my HP z820 12 core).

As for latency, there are several ways that it can creep into your session;
1-high-latency plugins(showing Delay Compensation will reveal that). The solutions include disabling plugins with latency until all tracking is done. For me, that's any plugin with more than 7-11 samples(so Delay Compensation isn't pushing stuff later to compensate) and any Master Track plugins with any latency(Master Track plugins are NOT compensated for, but you will still hear any latency present).

2-Erroneous Delay Compensation, which can be caused by a send that goes nowhere. An example of this is; you put a send on a track to feed a reverb/aux track. Then you changed your mind and deleted the aux track, but the send is still trying work(this one bit me a few times before I figured it out)

Back to the computer choking, what are you trying to record? If its audio tracks, I think the PC needs some help. Unless the session is massive(like 60+ tracks, in which case I would maybe bounce out a rough mix>import into the session>nudge it into alignment>make all original tracks inactive>do your overdubs (with a low buffer). When done, kill the rough mix track and reactivate all the others after pushing the buffer back up to 1024.

If you are tracking virtual instruments, then it may be the VI that is choking the system. Even on my 12-core, KeyScape would give me fits at low buffer settings. My solution is to use MiniGrand or Expand to record the midi(those are both light on resource use). Once the midi is recorded and edited, swap the VI back to the resource hog(KeyScape here), up the buffer to 1024 and COMMIT the VI track. Then you can make the instrument track inactive so it doesn't tax the system. Watching the System Usage Meter while adding VI plugins will usually reveal if any are big system hogs

In case anyone reading doesn't understand how Delay Compensation works, it simply looks at the track with the most latency, and makes all other tracks later to match. It doesn't make latency "go away", and as I said earlier, latency on a Master Tracks is not compensated for(which is usually okay)